How Memory Replay in Sleep Boosts Creative Problem-Solving

Abstract

Creative thought relies on the reorganisation of existing knowledge. Sleep is known to be important for creative thinking, but there is a debate about which sleep stage is most relevant, and why. We address this issue by proposing that rapid eye movement sleep, or 'REM', and non-REM sleep facilitate creativity in different ways. Memory replay mechanisms in non-REM can abstract rules from corpuses of learned information, while replay in REM may promote novel associations. We propose that the iterative interleaving of REM and non-REM across a night boosts the formation of complex knowledge frameworks, and allows these frameworks to be restructured, thus facilitating creative thought. We outline a hypothetical computational model which will allow explicit testing of these hypotheses.

Keywords: consolidation; creativity; memory; reactivation; replay; sleep.

Copyright © 2018. Published by Elsevier Ltd.

Figures

Figure 1.. The BiOtA Model.

(A,B) A simpler representation of the process also shown in detail in (C,D). (A) Consolidation of episodic memories of lessons in astronomy from teachers, books, and TV leads to formation of a semantic representation of the solar system in the neocortex (green spot on the purple 3D surface representing semantic knowledge space). (B) The new representation of the solar system is far away from pre-existing representations of the atom and of concentric circles in semantic space. If these schemas are replayed concurrently in REM sleep, the shared structure will be detected and semantic knowledge space will be restructured so they can be linked and mapped closer together. (C) Provides a more detailed representation of the above. In non-REM sleep the hippocampus controls replay in the neocortex (red arrow) ensuring that only memories relating to a specific state are replayed concurrently. Overlapping replay leads to potentiation of shared aspects of these memories, or gist abstraction. Forgetting may result in memory for only this gist (e.g., a basic schema). (D) In REM sleep the cortex replays salient schemas and PGO waves trigger activity in other randomly chosen schemas. This spreads across networks easily due to the high ACh, allowing coherence and resulting in a search process that allows detection of similarities between the target schema and cortical schemas stemming from very different tasks or experiences. When such commonalities are detected, novel links are formed between related concepts, leading to restructuring of semantic knowledge space. Abbreviations: Ach, acetylcholine; BiOtA, broader form of the information overlap to abstract framework; PGO, ponto-geniculo-occipital; REM, rapid eye movement.

Figure 2.. Memory Replay in Sleep.

(A) A rat traverses a track over about 20 s and encodes locations using hippocampal place cells (14 colour-coded units are shown). (B) The rat sleeps after running on the maze and a colour-coded Rasta plot shows the same place cells firing again in roughly the same order in which they were active during track running. Interestingly, the entire 20-s experience is replayed in about 200 ms during non-REM sleep. (C) A hypnogram showing a typical night of sleep, with sleep stages indicated on the y axis as: wake (W), REM with 4–9 Hz theta activity in the hippocampus, Stage 2 (N2) with a characteristic 14 Hz sleep spindle, and Stage 3 (N3) SWS. Time is on the x axis. Black ovals illustrate the morphology of slow oscillations, theta activity, and sleep spindles (from left to right). Abbreviations: REM, rapid eye movement; SWS, slow wave sleep.

Figure 3.. Hypothetical Parallel Distributed Processing Model of BiOtA.

External stimuli, such as knowledge about astronomy, stemming from episodic experiences with books, teachers, and TV are coded into the hippocampus during wake. Replay during subsequent non-REM sleep (blue arrow) leads to formation of an abstracted representation of the solar system (green circles) in the neocortex. During subsequent REM, this cortical representation is replayed concurrently with other (older) cortical representations, for example, that of concentric circles (set of four purple circles). Commonalities between the solar system and the concentric circles will be coded in a still more abstracted form in a deeper layer (light blue circles). Each time such a representation is formed there is scope for detection of further overlap with other existing memories (e.g., the memory for the atom, set of three purple circles), or with new incoming memories. Thus, repeated cycles of non-REM and REM allow the memory to be represented in a more and more abstracted/integrated manner. Abbreviations: BiOtA, broader form of the information overlap to abstract framework; NREM, non-rapid eye movement; REM, rapid eye movement.

Figure I.. How Can You Make Four Equilateral Triangles with Six Matches?

Solution: build a pyramid. Faulty representation is to constrain solutions to 2D; this solution can only be found in 3D.